Hey MJK, fellow new-ish reviewer here, just went through the indexing exercise on my own site so this is fresh.
Foundation looks solid — Astro, view-transitions, per-locale canonical and og:locale wired up right (checked /sr/). One big gap though: no hreflang tags anywhere in <head>. With 11 Balkan locales, Google currently sees them as 11 separate sites competing on translated content rather than alternates of the same content. Fixing that is probably the single highest-leverage thing you can do right now.
What it needs on every page:
Code:
<link rel="alternate" hreflang="en" href="https://balkasino.com/" />
<link rel="alternate" hreflang="sr" href="https://balkasino.com/sr/" />
<link rel="alternate" hreflang="hr" href="https://balkasino.com/hr/" />
...
Heads up your "/cnr/" for Montenegrin — Google doesn't recognise "cnr" as a hreflang code, use "sr-ME" or "bs-ME" depending on script.
On indexing — sitemap.xml to Search Console and Bing Webmaster Tools, manual "Inspect URL" requests for your top 10-20 pages. The "@astrojs/sitemap" package handles generation.
On links — avoid the obvious exchange schemes, they're a manual action waiting to happen in iGaming. Serpzilla has a real gambling-friendly marketplace but the inventory is hidden by default, you'll need to ping support to unlock it. GSA Search Engine Ranker for tier-2 diversity behind serious placements, not for direct ranking in 2026.
On performance — PageSpeed mobile is 84, TBT and CLS are perfect, LCP at 3.8s is what's holding you back. Preload the hero image and add the "fetchpriority=high" attribute on it, usually drops LCP under 2.5s without touching anything structural.
One genuine question while I have you — your top 24 list is heavy on offshore-licensed brands (Anjouan, Curaçao). Is that actually what Balkan players are picking, or is the list shaped more by which affiliate programs took you on early? Curious because it's a real choice with SEO consequences — local-licensed operators (Serbia's regulated market, etc.) would index differently and might be easier to rank against generic .com competitors. Not a criticism, just genuinely curious what you're seeing in your own data.
Good luck. 
PS — heads up that hreflang can also live inside sitemap.xml directly (via <xhtml:link rel="alternate" hreflang="..."> on each <url> entry) instead of in <head> — one of two valid Google implementations, pick whichever is easier to maintain.